FUEL TANK SHUTS OFF

You can't put more than a few dollars worth of gas in the car. We had the charcoal filter replaced and the lines that were kinked straightened out and we still have a problem. Hyundai dealers locally say it sounds like the shut off valve but I've read horror stories on line of people spending hundreds of dollars replacing all sorts of things and nothing working.

Any thoughts and any estimate as to how much replacing the shut off should cost?